(1) Field of the Invention
The present invention relates to a photosensitive polymer composition for a water developable flexographic printing plate and more particularly to a photosensitive polymer composition suitable for a solid photosensitive printing plate material which is developable with only neutral water and which affords a flexographic printing plate suitable for printing using a water-based ink.
(2) Description of the Prior Art
Photosensitive polymer compositions comprising an elastomer as a carrier component such as a chlorinated rubber, a styrene-butadiene block copolymer, or a polyurethane, as well as an ethylenically unsaturated compound and a photopolymerization initiator, are useful as flexographic printing plate materials, making the most of characteristics of the elastomer, and various proposals have been made as in U.S. Pat. Nos. 2,948,611 and 3,024,180 and Japanese Patent Publication No. 51-43374B.
Such solid photosensitive material for flexographing printing requires development using a halogenated hydrocarbon and involves problems such as health trouble and environmental pollution. Therefore, the development of a water developable, solid, photosensitive polymer for flexographic printing has been desired, and proposals are made with respect to photosensitive polymer compositions as materials for water developable, solid, photosensitive flexographic printing plates, for example, in U.S. Pat. Nos. 4,023,973; 4,177,074; 4,247,624; 4,272,608; 4,275,142; 4,415,649; 4,431,723; 4,446,220; 4,464,456; 4,517,279; and 4,689,290; and Japanese Patent Unexamined Publication (Kokai) No. 1-219735A.
However, it is difficult to satisfy all of high strength and water developability of a printing plate material, flexibility as a flexographic printing plate and adaptability to a water-based ink which is mainly used in flexographic printing. As such material of a printing plate there has not been obtained yet a satisfactory material in practical use. Particularly, in the development of a printing plate material, there has not been known a solid, photosensitive polymer material for a flexographic printing plate which exhibits a practical developability substantially in the use of neutral water alone.
In U.S. Pat. Nos. 4,889,793 and 4,927,739 it is shown that a water developable, solid, photosensitive, flexographic printing plate material is obtained from a photosensitive polymer composition prepared by solidifying a large amount of an ethylenically unsaturated compound with a polyamide as a polymeric gelling agent and/or a specific compound known usually as an oil gelling agent. However, by the methods described in these patents it has still been difficult to practically satisfy all of high strength and water developability of a printing plate material, flexibility as a flexographic printing plate and printability in the use of a water-base ink which is mainly used in flexographic printing.